SSL devices can have light emitting dies with different electrode configurations. For example, FIG. 1A is a cross-sectional view of a light emitting die 10 with lateral electrodes. As shown in FIG. 1A, the light emitting die 10 includes a substrate 12 carrying an LED structure 11 comprised of N-type gallium nitride (GaN) 14, GaN/indium gallium nitride (InGaN) multiple quantum wells (“MQWs”) 16, and P-type GaN 18. The light emitting die 10 also includes a first electrode 20 on the N-type GaN 14 and a second electrode 22 on the P-type GaN 18. As shown in FIG. 1A, the first and second electrodes 20 and 22 are both on the front side of the LED structure 11 and readily accessible.
FIG. 1B shows a light emitting die 10′ with vertical electrodes. The light emitting die 10′ includes a first electrode 20 on the N-type GaN 14 and second electrode 22 under the P-type GaN 18. The light emitting die 10′ can have higher degrees of current spreading between the first and second electrodes 20 and 22 than the light emitting die 10 of FIG. 1A. However, the second electrode 22 is not readily accessible because it is buried between the P-type GaN 18 and the substrate 12. In addition, the first electrode 20 partially blocks the generated light (as indicated by the arrow 15a), and thus only allows a portion of the generated light to be extracted (as indicated by the arrow 15b). Thus, the light extraction efficiency of the light emitting die 10′ may be limited.
One approach for improving the light extraction efficiency of light emitting dies with vertical electrodes is by incorporating a “buried” electrode. As shown in FIG. 1C, an light emitting die 10″ includes an opening 21 extending into the N-type GaN 14 from the substrate 12. An insulating material 25 lines the sidewalls 23 of the opening 21. A conductive material is disposed in the opening 21 to form the first electrode 20. The light emitting die 10″ with the buried first electrode 20 can have improved light extraction efficiencies because it does not cover any portion of the N-type GaN 14. However, neither of the first and second electrodes 20 and 22 are readily accessible in this design, and they require precise alignment with external conductors to avoid electrode mismatch. Accordingly, several improvements in electrode configuration of light emitting dies may be desirable.